This invention relates to an apparatus for cutting metal bars, such as bars used during construction to reinforce concrete, generally known as rebars, and in particular to such a device which is portable and can be used on the ground at construction sites.
U.S. Pat. No. 4,594,875, issued Jun. 17, 1986 to the inventor hereof, the disclosure of which is incorporated herein by reference, disclosed and claims an improved rebar bending machine which is lightweight, hand operated and adapted to be used in the field by a single person. It has a laterally stabilized, elongated base and, mounted to the base, a pair of spaced apart forming posts which straddle a slide mounted pair of lugs that form between them a groove into which rebar to be bent is placed. The slide is movable in an elongated guideway in a direction perpendicular to a line interconnecting the centers of the forming posts so that the groove defined by the lugs can be moved from a first position, at which a rebar placed in the groove is substantially tangent to the peripheries of the posts, past the line interconnecting the post centers, to a second position on the other side of the posts. In the course of this linear movement of the grooves a bend is formed in that portion of the rebar disposed between the lugs. Depending upon the length of travel of the lugs a bend of less than equal to or greater than 90 degrees is formed in the rebar although 90 degree bends are by far the most common.
That patent further disclosed to generate the relatively large bending forces with an elongated handle that is pivotally attached to the base. Suitable linkage connected to the handle and the slide translated the pivotal handle movements into linear slide motions.
To minimize the weight of the bending machine and to maximize the bending force, the slide, post and linkage are arranged so that the slide does not travel substantially more than the distance it must travel to effect the greatest bend in the bar, typically a bend of not more than about 120 degrees. In this manner, the overall length of the device in general and of the slide, base and guideway in particular can be minimized, which saves weight, labor and costs. Within a given size and configuration of the machine, the bending force that can be generated with the manually operated handle can be maximized. An effective, high speed and accurate bending of the rebar is thus possible with the device of that patent.
Bending machines constructed in accordance with the above-mentioned patent have been on sale for more than three years and have met with exceptional success. It is believed that the success is to a large extent attributable to its compact size, relatively low weight and to its easy operation even on the uneven ground frequently encountered at construction sites.
U.S. Pat. No. 4,794,779, issued Jan. 3, 1989 to the inventor hereof, the disclosure of which is incorporated herein by reference, significantly improves the usefulness of the bending machine disclosed in the above discussed '875 patent by making it possible to both bend originally straight bar and straighten bent rebar. This is achieved with no or only a negligible increase in the overall length of the machine and its weight, and without significantly increasing its costs.
Generally speaking the improved bending machine of patent No. '779 differs from the bending machine disclosed in the parent patent insofar as it provides the reciprocating slide with a second groove into which bent rebar to be straightened can be placed with, at the most, only a negligible increase in the overall travel length for the slide. The second groove is spaced from the first groove in the direction of slide travel (when bar placed in the first groove is being bent). The second groove is positioned so that bent rebar placed therein is approximately tangent to the peripheries of the forming posts on one side of the posts when straight rebar placed in the first groove is approximately tangent to the peripheries of the forming posts on the other side thereof.
As a result of this positional interrelationship between the first and second grooves the second groove is relatively remote from the forming posts when the slide has been moved the required distance to bend an originally straight bar placed in the first groove. Consequently, within these limits of slide travel a much greater distance is attained between the forming posts and the second groove than between the forming posts and the first groove. This significantly larger distance makes it possible to place a 90 degree bent rebar, for example, into simultaneous engagement with the peripheries of the posts and the second groove by locating the bent portion of the rebar in the second groove.
The bent rebar can be straightened by moving the slide in the opposite direction until the second groove is substantially tangent to the periphery of the posts.
The second groove can be constructed in any one of several configurations. It is important, however, to position the second groove as close as possible to the first groove to avoid interference with the pivot support for the handle which activates the slide, or conversely, to avoid the increase to the spacing between the forming posts and the handle pivot which would again increase the overall length of the device, its weight and cost. In its simplest form, the second groove can be defined by spaced apart, first and second lugs in substantially the same manner in which the first and second lugs of the first groove are constructed. In addition, the adjacent lugs for the two grooves can be combined into a single, double acting lug or post.
Bent rebar, when placed in the second groove, can pivot upwardly out of the groove, depending on the length of the bent rebar, the manner in which it is supported by the machine and/or the surrounding ground etc. The '779 invention also contemplates to constrain the bent rebar in the second groove against such upward movement. To accomplish this another embodiment of the invention defines the second groove partially with one of the lugs for the first groove and a hook, pivotally attached to the lug. The hook can be pivoted over the bent bar in the second groove so that a downwardly oriented free arm of the hook defines a portion of the second groove. Preferably, in this embodiment releasable lock means is provided to secure the hook in either its open or is closed position to prevent an accidental disengagement of the hook from the bar during the bar straightening operation.
Reference is also made to U.S. Pat. No. 4,798,078 and 4,887,447, issued to the present inventor, which adds a cutter to the parent Patent.